Conventionally, two methods of manufacturing have been employed to fabricate clutch cylinder-drum assemblies for use in automatic transmissions or transaxles of vehicle drivetrains. The first utilizes an electron beam weld method and the second involves integrally casting the assembly and machining it to a desired configuration. Each method has disadvantages and limitations.
The electron beam method is applied to a clutch cylinder and drum, each of which is generally formed through a stamping operation. The clutch cylinder includes an annular, radially extending base plate connected to an axially extending cylindrical member. The drum includes an annular, radially extending end plate adjoining an axially extending cylindrical wall. The clutch cylinder is placed within the drum, with the base plate abutting the end plate. An electron beam is directed to the inside of the clutch cylinder with the beam penetrating through the base and end plates. Alternatively, the electron beam is applied to the exterior of the end plate, penetrating into and through the end and base plates. Generally, due to the size and complexity of the electron beam welding apparatus, the components to be welded are rotated about a fixed welding apparatus to form an annular weld.
One disadvantage of this method is that electron beam welding typically requires a great deal of maintenance to keep the welding apparatus operating properly. Electron beam welding generally requires a vacuum chamber which reduces barometric pressure to the order of 1.times.10.sup.-1 to 1.times.10.sup.-2 Torr. (Atmospheric pressure is approximately 760 Torr). If air or other gases are present, the electron beam will scatter, thus deteriorating the effectiveness of the weld procedure. This high vacuum tends to draw metal vapors from workpieces, thereby requiring removal of these vapors. The voltage used across the workpieces is in the range of 30,000-200,000 volts, thus requiring an expensive power supply.
Second, the electron beam methods known to have been used to date have penetrated the inner or exposed surface of the annular base plate of the clutch cylinder. This produces warping, and weld spatter on this surface. Unless weld spatter is removed, at a later date it may break free and contaminate the transmission fluid. In turn, this may cause clogging in the flow of transmission fluid or a valve body located in the transmission or transaxle system. Further, these contaminants may increase wear to parts within the transmission or transaxle.
The warping of the exposed inner surface of the clutch cylinder may cause further problems. If the surface is not flat, a piston operating within the clutch cylinder may become ramped or cocked, allowing for fluid leakage or piston interference and seizure during operation of the transmission or transaxle. As other components of the transmission or transaxle often locate in relation to this surface, flatness of the exposed surface is required for their proper positioning. Consequently, an additional manufacturing step may be required to machine this surface to achieve a desired flatness.
Finally, the electron beam weld method uses X-ray radiation. This is potentially dangerous to operators, and, therefore, lead shielding or heavy sections of machine base castings are required around the welding apparatus. Shielding makes observation of the welding process more difficult, and interferes with steps involved in correcting problems associated with the welding apparatus and procedure. Also, in some States, official certification and inspections are required to operate an electron beam welder.
The second conventional method of manufacturing a clutch cylinder-drum assembly involves forming the assembly directly in cast iron and machining it to the proper configuration. This method also has a number of drawbacks.
First, cast iron is a more expensive material than the metal typically used to produce the stamped metal components. Second, facility and tooling costs are also greater. Cast iron requires a mold, is difficult to machine and in some instances, residue and chips remain after machining. These pieces may break free and contaminate the transmission fluid, thereby causing wear and clogging problems as discussed above. Finally, cast iron clutch cylinder-drum assemblies generally are significantly heavier than are those made of stamped metal components.
Methods for joining annular components together are known. One example is Nakayama et al, U.S. Pat. No. 3,949,186, which discloses a method using laser beam, electron beam or plasma welding techniques to join precision-machined hollow bodies to other metallic members. A concentrated beam of heat-producing energy is directed across and peripherally about the axially extending interface of the bodies to be joined. This reference suggests using the method for adjoining concentric precision machined wave guides for propagation of electromagnetic radiation.